In recent years, multiple input multiple output (MIMO) technology is primarily considered as one of technologies used in a next-generation mobile communication and wireless transmission system. The multiple input multiple output (MIMO) technology is a method for enhancing a spectral efficiency using multiple antennas to enhance a low spectral efficiency that has been a problem of the single input single output (SISO) method in the prior art.
The multiple input multiple output (MIMO) technology can be divided into a spatial multiplexing technique and a spatial diversity technique according to whether or not to transmit the same data.
The spatial multiplexing technique is a method for transmitting different data through several transmitting and receiving antennas at the same time. In other words, different data is transmitted through each transmitting antenna at the transmitter side, and suitable interference removal and signal processing is carried out for the received signals at the receiver side to obtain the transmitted data, thereby enhancing data transmission rate in proportion to the number of transmitting antennas.
The spatial diversity technique is a method for transmitting the same data through several transmitting antennas to obtain transmission diversity. In other words, the spatial diversity technique is a kind of space-time channel coding.
In such a spatial diversity technique, the same data is transmitted from several transmitting antennas, thereby greatly enhancing a transmission diversity gain. However, the spatial diversity technique is not a method for enhancing a transmission rate of data, but for enhancing the reliability of data transmission by enhancing a diversity gain.
Furthermore, the multiple input multiple output (MIMO) technology can be divided into an open loop method and a closed loop method according to whether information on channels is fed back from the receiver side to the transmitter side. Of them, the multiple input multiple output (MIMO) technology with a closed loop method may enhance a transmission rate of data using channel information fed back from the receiver side. For example, in a wireless communication system using the MIMO technology in a closed loop method, a base station at the transmission side receives a feedback on transmission channel information from a terminal at the receiving side, and transmits data using the information.
Of them, a collaborative multiple input multiple output method has been developed to reduce inter-cell interference in a multi-cell environment. Using the collaborative multiple input multiple output method, the terminal may receive data from a multi-cell base station in a collaborative manner.
In this case, each base station may support one or more terminals at the same time using the same frequency resource to enhance the performance of the system. Furthermore, the base station may perform a space division multiple access method based on configuration information on a channel between the base station and the terminal.
On the other hand, the coordinated multi-point (CoMP) transmission method has been developed to reduce inter-cell interference in a multi-cell environment and enhance the communication performance of a terminal located at an edge of the cell.
Using the CoMP method, the terminal may receive data from a multi-cell base station in a collaborative manner, thereby enhancing the communication performance of the terminal located at an edge of the cell. To this end, an accurate channel estimation based on a reference signal (RS) from the multi-cell base station may be required.
In the CoMP method, a cell-specific reference signal (CRS) may be used for measurement, and a demodulation reference signal may be used for demodulation.
In this case, CRS and DRS of cells performing the CoMP method, having a v-shift for each cell, may be transmitted to another location, or may have the same v-shift. Furthermore, CRS may be v-shifted, and DRS may be transmitted to the same location.
However, in the CoMP method in such a multi-cell environment, a collision between the reference signal (RS) and the resources element (RE) may occur, thereby causing a problem of channel estimation due to this, as well as causing a problem of pairing when applying a transmit diversity technique such as a space frequency block code (SFBC), a space time block code (STBC), and the like.
Accordingly, the foregoing problems that can occur while performing a CoMP operation in a multi-cell environment should be solved to more effectively perform the CoMP operation.